RichardL 
A single 36V 4AH battery is $249
From website
Pack includes 2 x 36V 4.0Ah Batteries
On-board LEDs display battery charge, temperature and troubleshooting prompts
Tapered design for easy grip, insertion and removal
Compatible with all RYOBI 36V garden tools
Orientated cell design inside for efficient heat management
Add more runtime to your RYOBI 36V garden tools at a value-packed price with the RYOBI 36V 4.0Ah Battery Twin Pack. Just one of these 36V Batteries provides enough power to mow a medium-sized lawn* with a RYOBi 36V Lawn mower. They’re also light enough to comfortably use with smaller RYOBI 36V handheld tools including leaf blowers, hedge trimmers and line trimmers.
These Batteries feature a slimmer, more tapered design compared to previous generations, making them easier to insert and remove from tools. Use the on-board LEDs to check battery charge status and get feedback on temperature and troubleshooting prompts. An orientated cell design inside the battery has been included to support heat management.
